Date: Tue, 12 Aug 1997 10:00:24 -0600 From: Steve Passe <smp@csn.net> To: cbrown@aracnet.com Cc: smp@FreeBSD.ORG Subject: Re: General smp & bios questions Message-ID: <199708121600.KAA19412@Ilsa.StevesCafe.com> In-Reply-To: Your message of "Mon, 11 Aug 1997 23:26:39 PDT." <33F0021F.49BFE86@earthling.net>
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Hi, > Using the "Through IO APIC" allows the I/O APIC to deliever > interrupts through the APIC bus. This is the prefered way of > doing things. Otherwise, interrupts are "hardwired" to a > particular processor. It doesn't matter too much since when > the system is put into full SMP mode, you will leave whichever > one you choose. Through the I/O APIC is closer to SMP :-). I have found this to be either untrue with some BIOS, or I don't know the magic to "make the crossover". Ie, I found it necessary to explicitly set "thru IO APIC" on my PR440FX. --- > Now, this would be a shame. This is a major scalibility limiter. > If possible, you should use the 2nd I/O APIC. Otherwise, you are > losing several interrupts and are crowding the ISA compatibility > interrupts unecessarily. > > > leave the second APIC disabled, and use "Through IO APIC" > > Any particular reason why? All of those extra interupts going to > waste? Because FreeBSD has a fundimental limit of 32 INT sources (they're stored in a int sized bitmask). I have about 90% of the code to support multiple APICs in place, but will have to do major surgery to get around the 32 source limit, there just isn't room in there to reference all the sources of 2 IO APICs + our software INTs: 24 + 24 + 4 + (more to come) -- Steve Passe | powered by smp@csn.net | Symmetric MultiProcessor FreeBSD
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